The use of glass reference cells filled with either a molecular gas or atomic vapor is a relatively old technology. Glass chambers or cells filled with gases or atom vapors are used by both commercial and military systems. Alkali metal filled glass cells such as those with rubidium, cesium, potassium, and sodium are used to frequency stabilize diode lasers. Molecular glass cells including acetylene, carbon monoxide, hydrogen cyanide, and methane cells, are the frequency reference standard for the telecom and gas sensing industry. These glass cells work well in a controlled environment but are not durable or stable enough for field use. Further, they are limited to absorption path lengths of 200 mm. In addition, they are fragile and bulky. There is a need for rugged and compact reference chambers with longer path lengths.